Steerable antenna system



March 10, 1970 s. LANDESMAN ET AL STEERABLE ANTENNA SYSTEM Filed Nov. 28, l966 3 Sheets-Sheet 1 March 10, 1970 Filed Nov. 28, 1966 s. LANDESMAN ETAL 3,500,427

STEERABLE ANTENNA SYSTEM 3 Sheets-Sheet 2 March 10, 1970 s. LANDESMAN ETAL 3,500,427

STEERABLE ANTENNA SYSTEM 3 Sheets-Sheet 3 Filed Nov. 28, 1966 U.S. Cl. 343-836 Claims ABSTRACT OF THE DISCLOSURE The number of necessary sources in an electronic scanning antenna system for scanning a given angular space portion with a beam having a given gain is reduced through associating a low gain scanning antenna system adapted for scanning a larger angular space portion than desired with a lower gain and an electromagnetic optical system having a high magnification ratio.

The present invention relates to antennas for scanning an angular space portion with a highly directive beam. More particularly, it relates to antennas with electronic scanning, formed by a panel of radiating elements excited with different phases. The dimensions of the panel depend, as is well known, on the gain to be obtained and on the operating wavelength.

The distance between radiating elements must be such that recombination lobes do not occur in undesired directions; it is smaller than the wavelength.

The number of radiating elements is therefore considerable, when the gain to be obtained is high, and this results in a complex antenna.

It is an object of this invention to provide an antenna of this type having a simplified structure and yet capable of performing the scanning of the limited solid angle.

According to the invention, there is provided a steerable antenna system for sweeping a first given angular space portion with a first radiation lobe having a high gain, said system comprising in association first aerial means comprising a plurality of radiating elements and controllable phase shifters, for sweeping a second given angular space portion greater than said first portion, with a lobe having a relatively low gain, and an electromagnetic optical system having a high magnification ratio.

For a better understanding of the invention reference will be made to the drawing accompanying the following description and in which:

FIG. 1 shows an embodiment of an application of the invention to an antenna with small electronic scanning in elevation and large in azimuth;

FIG. 2 is a diagram showing the principle of optics used in the ambodiment according to the invention;

FIG. 3a and 3b show in greater detail the arrangement of various elements of FIG. 1;

FIG. 4 shows diagrammatically the arrangement of the reflectors in another embodiment, and

FIG. 5 shows an example of a panel of radiating elements.

According to the invention, a small panel S of radiating elements capable of scanning a large solid angle (40", for example) but with low gain, is associated with an optical highfrequency system whose angular magnification makes it possible to obtain a limited scanning with a substantial gain.

This system may consist theoretically of two highfrequency lenses or of one lens and one reflector, or of two substantially cofocal reflectors. This last solution will be adopted normally and will be described and illustrated in the following.

States If it is desired to reduce the scanning range only in one angular coordinate (for example in elevation), two cylindrical reflectors are used; where the scanning is to be small both in elevation and in azimuth, parts of quadric surfaces are used as reflectors.

FIG. 1 is a section along the vertical plane of symmetry of an embodiment of an antenna according to the invention, in the case of a large scanning in azimuth and small scanning in elevation. The panel S of radiating elements has therefore a small height h and a comparatively large length (perpendicular to the plane of FIG. 1) so that in the azimuth, where the optical system does not cause any reduction in the range scanned by the radiating elements, the gain is high.

In this embodiment, the radiating elements are arranged in offset, and a small reflector r and a large reflector R are used.

These two reflectors are cylindrical.

The scanning in azimuth is obtained directly electronically, by creating a phase gradient between the radiating elements of the same horizontal row of the panel.

The scanning in elevation angle is effected both by electronic scanning and according to the principle of the telescope, as shown in FIG. 2.

In this figure, a source of parallel rays with the height d illuminates a focussing system L with the focal length 1, whose image focus coincides with the object focus of a second focussing system L with the focal length f. The emerging rays are parallel and seem to come from a source with the height f'/f is the magnification of the instrument. When the incident rays are inclined at an angle a, the intermediate image is formed at F and the emergent beam is inclined at the angle a. so that The telescope transforms the aperture in direct proportion to its magnification and the scanning angle in inverse proportion.

If G is the magnification of the optical system formed by the two reflectors, the effective scanning in elevation will be equal to 1/ G times the primary scanning, effected electronically for the panel of radiating elements and due to the vertical phase gradient, and the gain in elevation will be substantially equal to G times that of the panel of radiating elements along.

It may be seen that there is a problem of illumination: the illumination over the aperture is displaced with the scanning.

For the centre of allumination not to move, the directrix of the reflector r is substantially an ellipse with the foci and at the centre of the radiating elements on the one hand, and substantially at the centre of the main reflector R on the other hand, the directrix of reflector R being substantially parabolic.

Two arrangements are possible. These are shown FIG. 3a and FIG. 3b respectively.

In the case of a simple assembly of cylindrical reflectors and one panel in offset, as shown in FIG. 1, the

' arrangement of FIG. 3a is adopted, which permits to compensate the aberrations of the optical system.

For a low scanning in site and in azimuth, a square panel of small dimensions and reflectors formed by portions of second order surfaces will be adopted. FIG. 1 may therefore also be considered as a vertical cross-section of the antenna under the assumption that R and r are plane sections of a paraboloid and of an elipsoid, re-

3 spectively, and by reducing the length of the radiating element panel.

In FIGURE 5 is shown schematically a panel of radiating elements and phase-shifters which, in association with an electromagnet optical system of magnification equal to 5 is capable of scanning the space with a beam of 2 aperture in both direction over an azimuthal range of 50 and an elevation range of 10.

This panel, S, comprises twelve rows of each sixty radiating dipoles, respectively S to 5 S to 5 S to S and respective phase-shifters Ph to Ph associated respectively with said radiating elements. A panel of sixty rows of each sixty radiating elements, and as many phase-shifters would be required if the panel were to be used alone.

The arrows C and E respectively represents the phaseshifter control system and the energy feed of the radiating elements.

Naturally, the invention is not limited to the embodiment hereinbefore described.

More particularly, it should be noted that the oflset arrangement may be eliminated by using a semi-transparent reflector r and a reflector R causing a change in the direction of polarization, wherein the arrangement of FIG. 3b is utilized as shown in FIG. 4. It is also possible to use two optical assemblies arranged symetrically relative to the panel of radiating elements, wherein the reflectors, such as R, are associated with recombination prisms such as indicated in the patent application filed by the applicants on Mar. 23, 1966, Ser. No. 536,880, now U.S. Patent No. 3,430,246, Improved Two-reflectors Antenna.

In the latter case, there are again the advantages of the offset arrangement (absence of source shadow) without the drawbacks (rise of secondary lobes and loss of gain).

It should also be noted that the combination, according to the invention, of a large scanning-low gain system with a high magnification electromagnetic optical system, does not apply only to antenna systems of the type described, but also to any scanning antenna. Nevertheless, the invention has been described with reference to the former case, as it is of particularly high interest when antennas with electronic scanning are used, since the number of radiating elements and phase-shifters becomes rapidly prohibitive if the antenna is utilized along.

What is claimed is:

1. A steerable antenna system for sweeping a first given angular space portion with a first radiation lobe having a high gain, said system comprising in association first aerial means comprising a plurality of radiating sources and controllable phase-shifters, for sweeping a second given angular space portion greater than said first portion, with a lobe having a relatively low gain, and an electromagnetic optical system having a high magnification ratio comprising at least a first and a second elementary electromagnetic optical confocal device, said first device being located on the path of said lobe.

2. A system according to claim 1 wherein said first device is a relatively small reflector illuminated by said aerial means, and said second device is a relatively large reflector.

3. A system according to claim 1 wherein said optical system comprises elements which are constituted of portions of second order surfaces.

4. A system according to claim 1 wherein said optical system comprises elements which are constituted of portions of cylindrical surfaces.

5. The association of a steerable antenna system for sweeping a relatively large angular space portion with a lobe having a low gain, with an optical high frequency system having a high magnification ratio along at least one direction for obtaining the sweeping of a relatively small angular space portion with a lobe having a high gain, said optical system comprising at least a first and a second elementary electromagnetic optical device, said first device being located on the path of said lobe.

References Cited UNITED STATES PATENTS 9/1964 Hafner 343-753 X 2/1965 Rotman.

U.S. Cl. X.R. 

